Friday, May 30, 2014

High reflectance material poured down the walls toward the floor of Maskelyne B crater, indicating interbedding of high reflectance with low reflectance layers in its walls. Image field of view is 2800 meters, vertical relief across this view is 1300 meters in depth. LROC NAC mosaic M137360167LR, LRO orbit 5376, August 25, 2010; 35.77° incidence angle, resolution 51 cm from 47.04 km [NASA/GSFC/Arizona State University].

Aaron Boyd

LROC News System

Maskelyne B (8.34 km; 1.97°N, 28.96°E) is a simple crater in southern Mare Tranquillitatis, about 1800 meters deep across only 8 km. The stratigraphy revealed in the walls of the Maskelyne B impact crater are clues to the volcanic history in Mare Tranquillitatis.

Perhaps there is older, higher reflectance anorthositic material beneath younger and darker basaltic lava flows. Layering also occurs by large impacts ejecting and emplacing older subsurface material on the local terrain. The most likely cause for the layers seen in Maskelyne B is from the erosion of large coherent blocks of unexposed mare basalt over mature space-weathered regolith. High resolution spectral imaging or samples of this area would resolve this ambiguity.

The surface of Mare Tranquillitatis was built up over time by lava flows between 3.5 and 3.9 billion years ago creating stratigraphic units that are visible today. Maskelyne B formed long after the lava cooled. As the crater walls are eroded away by smaller impacts, the higher reflectance material is exposed and the surface is ground into boulders, cobbles, and dust.

High-resolution reproduction of the LROC NAC mosaic M137360167LR, and the northwest semicircle of Maskelyne B is available HERE [NASA/GSFC/Arizona State University].

The contrast between the light boulders and dark slopes draws the eye and piques curiosity to know what lies beneath the surface. See more of Maskelyne B and the surrounding area below.

Friday, May 23, 2014

Tracks made by Lunokhod 2 in 1976 as the Soviets tested for variations in the local magnetic field while traversing around a small crater (25.764°N, 30.474°E) inside le Monnier crater, on the eastern edge of Mare Serenitatis. From LROC NAC observation M122007650R, LRO orbit 3114, February 28, 2010; 36.59° incidence angle, resolution 50 cm from 43.89 km [NASA/ GSFC/ Arizona State University].

Mark Robinson

Principal Investigator

Lunar Reconnaissance Orbiter Camera

Arizona State University

On 15 January 1973, just one month after the successful Apollo 17 mission culminated the US Project Apollo, the Soviet Luna 21 spacecraft landed softly just 170 km north of the Apollo 17 site on the eastern margin of Mare Serenitatis.

A day later on 16 January the rover Lunokhod 2 disembarked and, on 18 January, with a full battery charge it circumnavigated and imaged its faithful lander and began its record-setting journey across the lunar landscape.

The eight-wheeled rover was operated by controllers in Simferopol, Crimea, mainly using a mast-mounted TV camera and ‘joystick’ controls and roved the lunar surface for five Earth months, surviving four bitterly cold lunar nights (as low as -150 °C (-240 °F)) and racking up about 39 km (~24.4 miles) of traverse distance.

The original reported distance was 37 km, which made Lunokhod 2 the planetary rover traverse distance record holder! Along its traverse, Lunokhod 2 carried out a series of scientific experiments that were not well publicized in the United States. Today’s Featured Image shows a cross-like pattern of rover tracks made as Lunokhod 2 explored a small crater, making various scientific measurements.

A typical Lunokhod operations crew included a commander, a navigator, a driver, an engineer, a radio/antenna operator, and one man in reserve.

Panorama taken by Lunokhod 2 at the crater shown in LROC NAC observation M122007650R (cropped from L2_D03_S03_P05m). The main experiments at this location were to test for changes in the local magnetic field due to the crater and characteristics of the regolith [Courtesy of Roskosmos and Russian Academy of Sciences].

Tracing the tracks in LROC NAC images, with new accurate geodetic controls that incorporate the latest topographic information from LROC and LOLA, the length of the Lunokhod 2 traverse is now accurately determined and is greater than the originally estimated 37 km. In fact, the intrepid Lunokhod 2 traversed approximately 39 km! The new traverse measurements were carried out by scientists at Moscow State University, and then again by a team at Washington University in St. Louis. The distance measurements follow the complete route shown by the tracks: including a “tripled” segment about 2 km in length, several long, linear magnetometer traverses, and several impact crater crossing maneuvers.

LROC NAC M122007650R, with portion of Lunokhod 2 rover tracks highlighted, where instruments gathered magnetometer measurements and did a triple traverse. Small circles can also be seen where the Lunokhod turned in place to take panoramic images [NASA/GSFC/Arizona State University].

Exploring Hilly Terrain

During the Lunokhod 2 mission, as the deputy leader of the Scientific Team and leader of the Geology Group, Dr. Alexander “Sasha” Basilevsky worked tirelessly to maximize the science return of the mission. Meeting this goal was not so easy because the Managing Group (Crew plus representatives of Lavochkin Association, which built the Lunokhods) was mostly thinking about demonstrating the roving and control capability of Lunokhod 2, and establishing a new distance record. Dr. Basilevsky recounts,

“So when moving south from the landing point, we crossed the mare area and reached a hilly terrain (low "highland" terrain). I was planning to study it and then to go north and then east towards a graben later called Fossa Recta. But the managing team did not like long sessions of TV stereo-imaging and other measurements, and they sent Lunokhod back to the north despite my protests.

Detail map of the SW portion of the Lunokhod 2 traverse. White box indicates the field of view shown at high-resolution in the LROC Featured Image released May 2014 [NASA/GSFC/Arizona State University].

“So I called to Moscow to the head of my laboratory, Professor Cyrill Florensky, he called to Vice President of Academy of Sciences Academician Alexander Vinogradov, and Vinogradov called Sergei Kryukov, the Lavochkin Association director, and explained that the hilly terrain had to be studied. Kryukov agreed and called to the Lunokhod Control Center in Crimea where we were and said, ‘please, follow the suggestion of that guy Basilevsky.’

“Meanwhile Lunokhod 2 proceeded quite a long way. After the Kryukov call worked, the crew just turned the vehicle back and then drove along the track. That was safe and they could be fast. When Lunokhod 2 came back to the hilly terrain station we made several panoramas, and then drove back to north along the double track and again could be fast.

“So the result was good for both sides of the [issue]: For science: we studied [the hilly] terrain, and for the Managing Group: Lunokhod made a lot of meters.”

At the conclusion of the ‘tripled’ traverse segment, Lunokhod 2 had racked up about 17 km of odometry. Controllers then began the long eastward drive to Fossa Recta (‘Straight Rille’), crossing Fossa Inconspicua (‘Unnoticed Rille’) along the way. Magnetometer experiments were done along the tripled traverse to test for effects related to the mare-highland boundary, and later, on the east and west sides of Fossa Recta (see below). Other observations and measurements included soil compositional analyses using an X-ray fluorescence spectrometer, soil mechanics experiments using a penetrometer, solar X-ray monitoring, a photodetector to detect UV light sources and the level of Earth-glow on the night-time Moon, laser ranging, 86 panorama photos, and some 80,000 TV pictures. The laser ranging retroreflector, a French instrument, is still in use today.

Fossa Recta Exploration

On its fourth lunar day of roving, Lunokhod 2 explored a linear depression (graben or rille), Fossa Recta. After approaching the depression, the Lunokhod was driven along a path leading away from its edge to measure any changes in the local magnetic field associated with the depression, and then back along the same path to the edge again. By reversing its direction and retracing its path, the effect of the Lunokhod, itself, on the magnetic signal could be determined and subtracted from the signal. A portion of the panorama taken by Lunokhod 2 when it approached the graben of Fossa Recta is shown below.

Part of the Panorama (L2_D04_S11_P09m) showing a portion of the Fossa Recta, stretching from north (left) to south (right) and a boulder field in the foreground. The sharp object on the left side of the panorama is the soil penetrometer [Courtesy of Roskosmos and Russian Academy of Sciences].

When the panorama was taken, Lunokhod 2 was on the western edge of Fossa Recta, at the position shown above, and boulders on the very edge of the depression are readily seen. The boulders were described in a paper by Basilevsky, Florensky, and Ronca (1977) in a scientific journal, The Moon, Vol. 17, and interpreted as boulders derived from lava bedrock at the edge of a long linear depression. The characteristics observed at the edge of the fossa are similar to those seen by Apollo 15 astronauts Dave Scott and Jim Irwin at Hadley Rille. After exploring Fossa Recta Lunokhod 2 was nowhere near done!

Lunar craters less than between approximately 15-20 km in size are usually bowl-shaped, so the crater above, excavating the floor of Abel C (41.5 km; 36.72°S, 82.5°E) has a somewhat irregular morphology relative to most craters of its size (about 100 meters).

This crater is characterized by its block-strewn, hummocky floor and low-relief rim. The step-like or benched appearance most evident in the northeastern portion of the wall is due to a strength discontinuity. Such discontinuity indicates that the impact penetrated through two materials of different strengths. Lab experiments have shown that the bench crater morphology forms when the surface layer is composed of thin and poorly consolidated regolith and the subsurface is composed of harder, more coherent material.

Small relatively fresh excavation, the 100 meter crater right of center shown in context of the full, 3.6 km-wide field of view swept up in LROC NAC observation M1153673248R, May 2, 2014 [NASA/GSFC/Arizona State University].

In some cases, the underlying material is bedrock, evidenced by an abundance of boulders. So, what did the impactor punch through at the surface? Usually regolith is the culprit, but further investigation of the floor of Abel C suggests that it may not be regolith alone.

Abel C is a 36 km diameter crater on the southeastern limb of the Moon, just off the northwest edge of Mare Australe, a large region dominated by volcanic activity. Clementine (1994) color ratio images are extremely useful in identifying nonmare deposits since non basaltic compositions tend to stick out when Clementine images are placed in the proper color space. Three bands (415 nm, 750 nm, and 1000 nm) from the Clementine UVVIS camera were used to create the false-color image below.

Clementine (1994) false color image of the Mare Australe region with Abel C off the western edge. The floor of Abel C appears more red than the surrounding highlands, along with a clear indication of similar pyroclastic exposure like the multiple indications within Mare Australe [NASA/GSFC/Arizona State University].

The three bands were ratioed to control the colors of the false-color image. The 750/415 ratio controls the red component, which is an indication of low titanium or high glass content as found in mature lunar regolith and to a greater degree pyroclastic deposits. The 750/1000 ratio controls the green component and is an indicator of the amount of iron on the surface. The 415/750 ratio controls the blue component and indicates high titanium or bright slopes and albedos. In the Clementine false-color image, Abel C stands out from the highlands and more closely resembles the nearby mare. The strong red component, combined with the low-reflectance, mantled floor seen in Abel C is indicative of a pyroclastic deposit.

This pyroclastic deposit encompasses approximately 190 km2 and has been identified in studies of pyroclastic deposits across the Moon (Compositional analyses of lunar pyroclastic deposits by Gaddis et al. 2003). Because pyroclastic deposits have a mantled appearance, they must be relatively thin. It's possible that the thin upper layer the impactor penetrated was partially composed of pyroclastics.

Rilles located in mare deposits can form by two mechanisms, channelized lava flow or lava tube collapse, often combined with tectonic stresses. They display three major morphologies: linear, arcuate, and sinuous.

Rima Krieger is a sinuous rille, meaning that its twists and turns resemble meandering rivers on Earth. Sinuous rilles are thought to have formed as lava became channelized on top of a thick lava flow, as seen at Vallis Schröteri, or as lava flowed across the surface and carved into the substrate.

A roll through four modern orthographic perspectives of Krieger (with 10 km Van Bisbroeck crater superpositioned on its south rim) and the narrow pass through the crater's west wall, where Rima Krieger begins. The region is dominated by its proximity to young Aristarchus crater to the southwest. A 42 km field of view with data contributed by the Lunar Orbiter series, Clementine and LRO [NASA/GSFC/Arizona State University].

In the case of Rima Krieger, some of the meanders occur at nearly right angles, suggesting that the flow was controlled to some degree by underlying structure. These sharp turns appear just outside the rim of Krieger. It's possible that the lava flow was diverted by structure resulting from the impact itself.

The rille and impact in Today's Featured Image are only a few of the fascinating formations in this region. Rima Krieger is located in one of the most geologically diverse regions of the Moon. To its west, the Aristarchus Plateau stands above the surrounding mare. On the Aristarchus Plateau, we see mare basalts juxtaposed with anorthositic materials excavated by the Aristarchus impact and a dark mantle of pyroclastics over much of the plateau.

Telescopic mosaic from Earth at full Moon, stretched for color contrast, shows some of the wide variety of basalt in north Procellarum, and just how Krieger (arrow) overpowered by its young neighbor, bright Copernican age Aristarchus and its excavation of Aristarchus plateau.

Local evening view de-emphasizes albedo and emphasizes terrain relief in this telescopic look at a 630 km field of view from Krieger (arrow, north) and Marius. (note the Marius Hills as their low profiles come into view on their namesake's north-northwest. Even the long Marius sinuous rille can be seen winding through the plain just north of those Hills. Krieger's morphology is still dominated by Aristarchus. Late crescent Moon mosaic by Astronominsk, September 25, 2008.

Very reduced view of the full-size ASTRONOMINSK late crescent Moon mosaic of 22 images, showing the field of view immediately above in context (inset). Note the differing perspectives on the Aristarchus Plateau, seen from Earth under a high and low Sun due to libration. The full mosaic can be viewed at the ASTRONOMINSK website, HERE.

Friday, May 16, 2014

An early morning view looking east-to-west from an altitude of 86 km across the southern portion of the Lassell Massif, an irregularly shaped series of hills and steep-walled depressions. North is to the right in this LROC NAC oblique mosaic M1108311369LR, LRO orbit 15611, November 23, 2012; 71.73° incidence angle, spacecraft and camera slew 56.64° from orbital nadir, resolution above 2 meters from 85.65 km over 14.63°S, 355.69°E [NASA/GSFC/Arizona State University].

J. Stopar

LROC News System

The Lassell Massif is a complex area of rugged terrain located in northeastern Mare Nubium (14.7°S, 351.0°E). This undulating terrain of hills and steep-walled depressions is 45 km across from north to south and 25 km across from east to west.

The southern portion of the massif comprises several prominent elongate depressions (like Lassell K and Lassell G, seen below) that are clustered together.

The Lassell Massif in Mare Nubium; north is to the right. Prominent features of the Lassell Massif region include Lassell C, K, and G [NASA/GSFC/Arizona State University].

The clustering and irregular shape of these negative-relief features is reminiscent of volcanic calderas on Earth and other terrestrial planets, including Mars. Calderas generally form through collapse as magma retreats from the vent area. Overlapping collapse features suggest multiple episodes of magma advance and retreat over time. Lassell K and G may be part of a volcanic caldera!

Lassell K and G could, however, instead represent a series of clustered impact craters, which are relatively common on the Moon.

Remote sensing data displayed in eight diverse views of the 1000 meter-high profile of Lassell massif, collected by four spacecraft (all of them post-Apollo) presented in an overlapping 40.2 km-wide field of view, visible throughout both day and night. The largest crater at center-left is Lassell C (8.74 km; 14.67°S, 350.64°E) [Clementine, LRO, Chandrayaan-1 and Chang'e-2].

Lassell K (left) and portion of Lassell G (right). The upper walls of these steep-walled depressions have dark, low-reflectance, boulders and downslope streamers (arrows), where a thin layer of dark material, possibly pyroclastic, has eroded out of the wall [NASA/GSFC/Arizona State University].

Looking closely at this region, we see other features that are typical of volcanic eruptions including: dark mantling layers interpreted as possible pyroclastics, a subdued or mantled terrain, and even a possible volcanic cone.

Taken together, these features suggest a complex volcanic history for this region. If the Lassell Massif is constructed from a series of volcanic extrusions, it may represent an unusual type of silicic volcanism on the Moon (perhaps similar in composition to rhyolite).

The full oblique image (below) along with other images and compositional data sets may reveal more clues to the timing and nature of volcanism in the Lassell region. However, returning rock samples to Earth and exploring the slopes of this structure from the surface may be the only way to confirm its origins.

View assorted sizes of an unlabeled sample of a mosaic from the LROC observation above, HERE.

This picture graced the covers of newspapers and magazines everywhere; it inspired a million words of prose and created the modern environmental movement as we know it. Few single images have had such pervasive and lasting power.

Apollo 8's overview effect: Iconic Earthrise image, AS08-14-2383, Bill Anders' serendipitous photograph of Earth as the first manned flight to the Moon swung around from the farside, December 24, 1968 [NASA/JSC].

The Apollo 11 crew landed on the lunar surface a few months after that Earthrise photo was circulated. During this and subsequent missions (all on the central near side of the Moon), it was reported by the media that Earth always appears stationary in the same part of the sky as seen from the Moon’s surface.

Simulated time-lapse view of Earth from the vicinity of the Moon's north pole, where the significance of the Moon's libration creates changes in a notional viewers perspective. Earth appears to swing through a Lissajous figure in the sky. Three lunar days are squeezed into 1:45 using Celesta.

Because the Moon orbits the Earth and is in synchronous rotation with its orbital period, we always see the same side. Hence, there is a near side (the hemisphere we see from Earth) and a far side (the side we cannot see from Earth; it is often mistakenly called the “dark side”).

A consequence of this synchronous rotation is that from the Moon, the Earth appears stationary in the sky, just as the hub of a bicycle wheel remains stationary from the viewpoint of one of its spokes. Thus, while the Sun rises and sets according to the slow rotation rate of the Moon (one complete rotation every 708 hours, half day and half night), the Earth is always in the same spot in the sky. Of course, because it is illuminated by the Sun, it changes its phase on the same timescale as does the Moon as seen from Earth, although reversed (a full Moon on Earth is a new Earth from the Moon and vice versa.) From the far side of the Moon, one does not see the Earth at all.

Are spectacular views of Earthrise only visible from spacecraft in orbit about the Moon? Not quite.

Two points about the Moon’s orbit make the story a bit more complicated. First, the Moon’s orbit around the Earth is not circular but elliptical, its distance ranging from 363,000 km up to 405,000 km from the Earth. Second, the plane of the Moon’s orbit is inclined about 5 degrees to the ecliptic (the plane of the Earth-Moon system’s orbit around the Sun). These two facts mean that the Moon librates, or “wobbles” both left and right (an effect of its elliptical orbit) and up and down (an effect of the inclination of its orbital plane). These librations are not overwhelmingly significant, but result in some interesting effects around the limb of the Moon – the great circle made up by the 90 degrees east and west longitude lines, including both poles.

Earthset, from 1080p video captured from Japan's lunar orbiter SELENE-1 (Kaguya) October 31, 2007, as spacecraft and camera, in polar orbit, began its track north from the south pole (on the rim of Shackleton crater, center left) over the Moon's farside, leaving Earth to set behind Malapert massif, a nearside fragment of the rim of immense South Pole-Aitken impact basin [JAXA/NHK/SELENE].

The Earth as seen from the Moon is about 2 degrees in angular width (about 4 times the apparent diameter of the Moon and Sun as seen from Earth). Earth’s disk is roughly equivalent to the size of a quarter held out at arm’s length; the Moon’s apparent disk is pea-sized. Because of the Moon’s longitudinal libration, the “limb” areas near the 90 degree meridians are sometimes visible to Earth and other times not. Thus, the Earth will sometimes appear in the sky and sometimes be hidden below the Moon’s horizon – in other words, an observer along this line of longitude will see an Earthrise and an Earthset.

The longitudinal libration is about 8 degrees, so the observer on the lunar limb would see the Earth slowly rise above the horizon and clear it by its apparent diameter, then slowly sink below the horizon by the same amount. That Earthrise will be slow indeed – it will take a couple of days for the full disk of the Earth to rise above the horizon. This cycle would repeat on a monthly timescale, as the Moon completes one revolution around the Earth.

Similarly, one would also see the Earth rise and set at the poles of the Moon, although to a different magnitude. The polar view is almost completely dominated by the latitudinal libration, caused by the inclination of the Moon’s orbital plane. This variation is about 6.5 degrees (it includes the Moon’s spin axis obliquity of 1.5 degrees) and would vary on a similar monthly timescale. These variations will become important if future lunar inhabitants live at the poles, as I think likely. As the Earth will sometimes be out of direct view, it is likely that we will depend on relay satellites for continuous communication. Polar inhabitants will also see a “different” Sun from what they’re accustomed to on Earth – at the lunar poles, the sun rotates around the horizon, rather than rising and setting.

Cernan and Earth. At Taurus Littrow, Earth maintains its position. Ground controllers did occasionally admonished Apollo 17 Cmdr. Gene Cernan's partner Jack Schmidt for lifting his solar visor to get a better look at a rock, from time to time, during the last walks on the Moon. But at this point, however, as he traded poses with Schmidt using Earth as a backdrop, Cernan did briefly lift his visor halfway, allowing posterity an atypical view of an actual human face on the Moon in December 1972 (AS17-134-20471) [NASA/JSC].

Thus, there are places on the Moon from which we can stand and contemplate the sheer beauty and magnificence of a slowly rising Earth. Given the sea change in global perspective provided by the famous Earthrise picture taken by the Apollo 8 crew almost fifty years ago, what societal impacts will occur when a human being stands on the lunar surface and watches the Earth slowly rise above the horizon? I suspect that a similar shift in planetary perspective will occur. If history is any guide, such a shift will have profound psychological and political implications – both positive and negative – in our reach for the stars.

Dr. Paul D. Spudis is a senior staff scientist at the Lunar and Planetary Institute in Houston. This column was originally published by Smithsonian Air & Space online, and his website can be found at www.spudislunarresources.com. The opinions he expressed here are his own, but these are better informed than most.

Larmor Q (28.674°N, 176.32°E) is sub-circular crater, whose 23 km diameter is measured north to south and 19 km measured east to west.

But Larmor Q is not just another stunning crater; it is also scientifically interesting. Oblique images, like the one below, provide a unique vantage point that can help with geologic interpretation.

Oblique view (reduced for web-browsing) of Larmor Q crater, looking east-to-west. The crater is wider in the north-south direction than in the east-west direction. Click for larger image [NASA/GSFC/Arizona State University].

One of the most obvious features of Larmor Q is the large accumulation of slumped wall materials inside the crater. This crater is a transitional morphology between smaller simple craters like this one, HERE, and larger, complex craters like Tycho or Copernicus.

The crater Giordano Bruno (21 km in diameter) is another example of a transitional crater. Wall slumping in transitional craters affects the final crater shape. When the northern wall of Larmor Q failed, the northern rim crest of the crater moved outward, contributing to the larger crater diameter in the north-south direction.

Prominent features of Larmor Q include slumped wall material and impact melt deposits; located at 176.313°E, 28.634°N [NASA/GSFC/Arizona State University].

This oblique image of Larmor Q is also useful for studying the distribution of impact melt, which, in turn, can tell us how impact melt is generated and interacts with the forming crater. In Larmor Q, most of the impact melt rock is located inside the crater opposite the largest slumped materials.

View of impact melt deposits inside Larmor Q. The melt has splashed up the southern wall (left) and ponded in the floor of the crater (center of image)[NASA/GSFC/Arizona State University].

Flows of impact melt on the rim of Larmor Q crater now solidified into lobate deposits [NASA/GSFC/Arizona State University].

There are also several relatively small deposits (flows) of impact melt rock on the crater rim. Because the largest concentration of impact melt occurs opposite the largest slumped materials, we infer that the melt “splashed” up on the southern wall primarily as a result of the slumped material impinging on the crater floor.

LRO experiences twelve earthrises every day, however LROC is almost always busy imaging the lunar surface so only rarely does an opportunity arise such that LROC can capture a view of the Earth. On the first of February of this year LRO pitched forward while approaching the north pole allowing the LROC WAC to capture the Earth rising above Rozhdestvenskiy crater (181 km; 85°N, 202.1°E).

The LROC Wide Angle Camera (WAC) is very different than most digital cameras. Typically resolution is reported as the number pixels in a single image, a cell phone camera today has more than 5 million pixels (5 megapixels). A single WAC frame has only 9856 pixels, however the WAC builds up a much larger image by exposing a series of images (or frames) as LRO progresses in its orbit; this type of imaging is called "push-frame". Over a full month as the LRO orbit track progresses around the Moon the WAC builds up a collection of images that covers the entire globe.

Occasionally LRO points off into space to acquire observations of the exosphere and perform instrument calibration measurements. During these slews sometimes the Earth (and other planets) pass through the WAC's field of view and dramatic images such as the one shown here are acquired. In the opening image the Moon is a grayscale composite of the first six frames of the WAC observation (while the spacecraft was still actively slewing), using visible bands 604 nm, 643 nm, and 689 nm. The Earth is a color composite of later frames, using the 415 nm, 566 nm, and 604 nm bands as blue, green, and red, respectively. These wavelengths were picked as they match well the response of the human eye, so the colors are very close to true, that is what the average person might see. Also, in this image the relative brightness between the Earth and the Moon is correct, note how much brighter the Earth is relative to the Moon.

LROC WAC Earthrise [NASA/GSFC/Arizona State University].

In the video the "venetian blind" banding demonstrates how a WAC image is built up frame-by-frame. The gaps between the frames are due to the real separation of the WAC filters on the CCD. The longest wavelength (689 nm) band is at the bottom of the scene, and the shortest (415 nm) is at the top; note how the Earth is brighter when it enters the top band due to the blue from the ocean. The frames were acquired at two second intervals, so the total time to collect the sequence was 5 minutes. The video is faster than reality by a factor of ~20.

Thursday, May 1, 2014

Wall and Rim of Arago E: Full resolution sample from and unusually low-altitude, LROC Narrow Angle Camera (NAC) observation from only 40 km altitude. The sample above shows detail of the northeast wall and floor of Arago E, an excavation of the complex Arago area of western Mare Tranquillitatis. The floor is peppered with boulders that have tumbled down the crater wall. This roughly 800 meter sq. field of view was cropped from LROC NAC M155084711R, LRO orbit 7989, March 18, 2011; resolution 47 cm per pixel, angle of incidence 10° from 40.02 km [NASA/GSFC/Arizona State University].

Raquel Nuno
LROC News System

Arago E (8.5°N ,22.71E°) is an elongated crater located in Mare Tranquillitatis, north of the July 1969 landing site of Apollo 11.

An unusually shaped crater, Arago E is nestled between two wrinkle ridges (see Wide Angle Camera context image below), tectonic features formed by the deformation of the basaltic rocks that make up the lunar maria.

Massive maria lavas placed an extra load on the surface, and these deformations are adjustments of the surface due to the unrelenting force of gravity buckling the rock.

Mosaic from the left and right LROC NAC cameras, LROC NAC observation M155084711R and L, allowing a wider look at the 3.7 km c 6.7 km interior of Arago E. View the original (1000 x 1710) reproduction HERE [NASA/GSFC/Arizona State University].

Elongated Arago E and the ruffled surface of west Tranquillitatis: High angle, early morning illumination highlights the undulations of the Tranquillitatis terrain between 25.5 km Arago, at lower left (6.15°N, 21.43°E) and the elongated, still partially shadowed interior of Arago E at upper center in this roughly 75 km-wide field of view from a mosaic made from two sequential LROC Wide Angle Camera passes, in orbits 6772 and 6773, December 13, 2010. 60 meters per pixel resolution, angle of incidence 74° from 44 km. View the original reproduction (1223 x 1951) HERE [NASA/GSFC/Arizona State University].

This crater's elongated shape is perhaps due to an oblique impact, which impart excess horizontal momentum into the surface leaving an elongated shape. However, for this to happen it's thought a progenitor projectile had to have been arriving from less than 30° above the horizon.

Volcanic vents can also display elongated shapes but don't exhibit raised rims and usually lack a flat floor from pooled impact melt, and both features are seen in Arago E.

Earthview context for Arago E: Arago and Arago E are familiar landmarks in telescopic views from Earth. With only a little practice, even amateurs, using modest telescopes can pick them out and, in their mind's eye at least, also pick out the relatively nearby landing sites of Apollo 11 and Apollo 17, the first and the last Apollo surface expeditions. The full-scale mosaic (inset) was "stacked" from ten frames April 21, 2010 by Yuri Goryachko, Mikhail Abgarian & Konstantin Morozov of Belarus [Astronominsk].

A picture of this crater was taken from orbit during the Apollo 15 mission. (You can see it HERE.) How does the LROC NAC observation, at full resolution HERE, compare?